High thermal conductivity disk brakes

ABSTRACT

An automotive disk brake assembly installed in an automobile having a wheel. The assembly includes a floating caliper supporting inner and outer brake pads and a brake rotor having a disk, a hat, wherein the hat is bolted to the wheel. A hydraulic cylinder pushes the inner brake pads into the disk surface, thereby causing the floating caliper to move so as to bring the outer brake pad into contact with the disk surfaces. Finally, the rotor is made of a material having a thickness and a coefficient of thermal expansion and conductivity, such that a complete 100 kilometer per hour, 0.9 gross vehicle weight braking causes the disk to expand in thickness by at least 0.10 mm and to cool to shrink in thickness, from its expanded thickness, by at least 0.05 mm within 60 seconds of cessation of braking, in an ambient temperature of less than 30° C.

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.13/449,505 filed Apr. 18, 2012, which is incorporated herein byreference as if fully set forth herein.

BACKGROUND

Currently, most motor vehicles are equipped with disk brakes, in which ametal, carbon or ceramic disk is rigidly affixed to a car wheel. Tocause braking, a pair of pads, one on either side of the disk, ispressed onto the surface of the disk, causing friction and slowing thevehicle. One challenge in the design of disk brakes is the need toabsorb and dissipate the great amount of heat that is generated, as thekinetic energy of the vehicle is converted to heat energy by brakefriction.

In currently available disk brakes systems, the heat of braking isabsorbed by the material mass between the two rubbing surfaces of eachdisk. This heat is dissipated, as the disk spins, through a) airconvection on the two rubbing surfaces, b) air convection in ventilationpassageways cast into the disk, and c) heat radiation of the two rubbingsurfaces, if the surfaces become red hot. A high surface temperaturereduces a brake pad's life and friction coefficient dramatically, and istherefore highly undesirable.

Another problem encountered with disk brakes is that of incomplete outerbrake pad disengagement after braking. Although the inner brake pad isaffirmatively withdrawn a slight distance (0.15 mm), the outer brake padtends to gently rub against the disk, after braking. This reduces fuelefficiency.

Also, as in any automotive component, the weight of a disk brake must becarried by the vehicle, so that any reduction in weight is desirable.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

In a first separate aspect, the present invention may take the form ofan automotive disk brake assembly installed in an automobile having awheel. The assembly includes a floating caliper supporting an inner andouter brake pad and a brake rotor having a disk, and a hat, and whereinthe hat is bolted to the wheel. A hydraulic cylinder is adapted to pushthe inner brake pads into the disk surface, thereby causing the floatingcaliper to move so as to bring the outer brake pad into contact with thedisk surfaces. Finally, the rotor is made at least in part of a materialhaving a thickness and a coefficient of thermal expansion and a thermalconductivity, such that a complete 100 kilometer per hour, 0.9 grossvehicle weight braking causes the disk to expand in thickness by atleast 0.1 mm and to cool to shrink in thickness, relative to itsexpanded thickness, by at least 0.05 mm within 60 seconds of thecessation of braking, in an ambient temperature of less than 30° C.

In a second separate aspect, the present invention may take the form ofa disc brake rotor that includes a mounting hat and a solid disc,rigidly affixed to the mounting hat. The solid disk has a transversedimension core, made of a first metal and two rubbing-surface claddings,set on either transverse side of the core, the claddings made of asecond metal and having a thickness of 1-10 mm, and further definingphysical engagement features. Also, a third metal is interposed betweenthe first metal and the second metal, such that the second metal isbonded with the first metal metallurgically through the third metal andmechanically by the engagement features.

In a third separate aspect, the present invention may take the form of amethod of fabricating a disk for a disk brake system. The method startsby the formation of a cladding workpiece having a first major externalsurface defining engagement features. Then the first major externalsurface is coated with a second metal. A mold is provided, defining aninterior shape of a rotor and the cladding workpiece is inserted intothe mold. A molten third metal is into the mold so that it engages tothe engagement features and reacts with the second metal and ispermitted to cool, thereby forming a disk made of the third metal, whichis metallurgically bonded and mechanically interlocked to the claddingworkpiece.

In a fourth separate aspect, the present invention may take the form ofa disk braking system having a rotor that has a conductance of greaterthan 2 Watts/° C.

In a fifth separate aspect, the present invention may take the form of adisk braking system having a rotor hat that has a conductance of greaterthan 4 Watts/° C.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced drawings. It isintended that the embodiments and figures disclosed herein are to beconsidered illustrative rather than restrictive.

FIG. 1 shows a cross-sectional view of a disk braking assembly having adisk attached to an automobile wheel.

FIG. 2 shows a plan view of a cladding workpiece that is incorporatedinto the assembly of FIG. 1.

FIG. 2 a shows a detail view of a portion of FIG. 2, indicated by circle2 a.

FIG. 3 shows a plan view of three of the cladding workpieces of FIG. 2,shown arranged as in the disk, and oriented so that the side facing intothe disk is shown.

FIG. 3 a shows a plan view of an alternative embodiment of claddingworkpieces of FIG. 3.

FIG. 3 b shows a plan view of another embodiment of cladding workpiecesof FIG. 3.

FIG. 4 shows a cross-sectional view of the rotor of the assembly of FIG.1.

FIG. 4 a shows a detail view of the rotor of FIG. 4, as indicated bycircle 4 a of FIG. 4.

FIG. 4 b shows a detail view of an alternative embodiment of the rotorof FIG. 4.

FIG. 5 shows a plan view of an alternative embodiment of the rotor ofFIG. 4.

FIG. 6 shows a cross-sectional view of the wheel-disk-axle junction ofan alternative embodiment of the assembly of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definition

In this application the term “inward” means toward the longitudinalcenter line of a vehicle in which the brake assembly is installed orinto which it will be installed, and “outward” means away from thiscenterline.

Referring to FIGS. 1 and 4, a brake assembly 8, includes a brake rotor10, which includes a disk 11 and a mounting hat 12, made up of amounting hat side wall 12′ and a mounting hat top wall 12″ (see FIG. 4)mounted on a vehicle wheel 13.

A floating caliper 14, defines a hydraulic cylinder 16 into which apiston 18 is set. An inner brake pad 20 is mounted on piston 18, suchthat when piston 18 is pushed outwardly from cylinder 16, inner brakepad 20 contacts disk 11. This in turn causes caliper 14 to be pulledinwardly so that an outer brake pad 22, held by caliper 14 contacts disk11.

In currently available brake assemblies, when braking is no longerapplied, the inner brake pad 20 retracts slightly, but the outer brakepad 22 does not necessarily retract adequately, and may continue tocontact the rotor, causing a drag on movement and reducing fuelefficiency. In brake assembly 8, however, rotor 10 is made in part of ametal that has a high coefficient of thermal expansion and a highthermal conductivity, so that disk 11 expands during braking. Heat isthen quickly conducted away by hat 12 into wheel 13, so that disk 11shrinks when braking is no longer applied. As a result, outer brake pad22 is not positioned as far inward as it would be if not for the disk 11expansion, and when disk 11 contracts, it withdraws from contact ofouter brake pad 22, thereby avoiding the problems caused by thiscontact. The other alternative in addressing the problem of the outerpad 22 not retracting sufficiently after braking would be to enlarge thespread of the caliper 14, thereby spreading the pads 20 and 22 apart.This, however, worsens the brake pedal response, forcing the driver topress the brake pedal down farther before braking begins. The slightlyslower braking response would add to the number of automobile accidentsoccurring every year.

Many aluminum alloys have the thermal properties required to effectuatethe present invention. These are a high coefficient of thermal expansionand high thermal conductivity (such as A308, A355, A356, A357, A443,A514, A850, and pure aluminum). Unfortunately, however, aluminum alloysare typically too soft to use in a brake rotor. In a preferredembodiment this problem is addressed by providing a steel cladding 30affirmatively attached to a second metal disk core 32. The rotor 10 isconnected to a wheel 13 made of a material with high thermalconductivity and high specific heat such as an aluminum alloy. In orderto maximize the flow of heat through and out of rotor 10, it is solid(as opposed to vented) and the thickness of the mounting hat side wall12′ is greater than 0.024 of disk 11 diameter, preferably much greaterif the brake assembly space allows, the mounting hat height should belower, preferably less than 5 cm for a front disk brake, or less than 8times of the thickness of the mounting hat side wall, the mounting hatouter diameter is greater than 0.5 of disk 11 outer diameter, and thediameter of the contact area 5 between the mounting hat 12 and the wheel13 is preferably equal to the mounting hat outer diameter. If not, athermal coupler can be designed, fabricated and installed to increasethe contact area, therefore, the heat transfer from the mounting hat tothe wheel. A thermal conductive paste can be applied between themounting hat and the wheel contact to further improve heat transfer.

Equation (1) describes the theoretical temperature increase in ° C., ofa front disk brake (which generates the bulk of the heat in anautomobile, relative to the rear brakes).

$\begin{matrix}{T_{th} = {\frac{\left( {1 - \Theta} \right)}{2}\left\lbrack \frac{W\left( {V_{1}^{2} - V_{2}^{2}} \right)}{2{g\left( {{\rho_{r}c_{r}v_{r}} + {\rho_{c}c_{c}v_{c}}} \right)}} \right\rbrack}} & (1)\end{matrix}$

Where

T_(th)=theoretical temperature increase, ° C.

φ=the percentage rear braking

W=vehicle weight, kg

V₁=initial velocity, m/s

V₂=final velocity, m/s

g=gravitational constant, 9.8 m/s²

ρ_(r)=rotor body material density, kg/m³

c_(r)=rotor body material specific heat capacity, J/kg° C.

ν_(r)=rotor body material volume, m³

ρ_(c)=clad material density, kg/m³

c_(c)=clad material specific heat capacity, J/kg° C.

ν_(c)=clad material volume, m³

In addition, we can define the following two quantities, the conductanceof the rotor (Conductance_(rotor)) and the conductance of the hat(Conductance_(hat)), using the parameters defined for the.

${Conductance}_{rotor} = \frac{k_{r}A_{cross}}{H_{hat} + {Th}_{1\text{/}2d} + D_{d - h}}$

One braking system design goal is to limit the theoretical temperatureincrease to less than 230° C. after a complete stop from 100 kph. Theuse of a brake body material with high specific heat and a solid diskbrake help to meet this goal. Aluminum and its alloys are good candidatematerials for this application.

The calculation for heat dissipation from a traditional vented diskbrake is based on the sum of convective cooling of rubbing surfaces,convective cooling of ventilation surfaces, and radiative cooling ofrubbing surfaces. The disk brake disclosed in this application is of asolid type, and has the same convective cooling and radiative cooling ofrubbing surfaces, but replaces the convective cooling of ventilationsurfaces (Eq. 2) with conductive cooling to a connected metal wheel (Eq.3).

q _(vent) =h _(vent) A _(vent)(T _(r) −T _(∞))  (2)

Where

q_(vent)=heat dissipation by convection at ventilation surfaces,Joules/hour

h_(vent)=heat transfer coefficient of convection at ventilationsurfaces, Joules/(hour*m²*° C.)

A_(vent)=ventilation surface area, m²

T_(r)=rotor body temperature, ° C.

T_(∞)=ambient temperature, ° C.

h=hours

q _(cond) =k _(r) A _(cross)(T _(r) −T _(wh-c))/(H _(hat) +Th _(1/2d) +D_(d-h))  (3)

Where

q_(cond)=heat dissipation by conduction to metal wheel, J/h

k_(r)=rotor body thermal conductivity, J/(h m ° C.)

A_(cross)=cross section area of rotor mounting hat side wall, m²

T_(r)=rotor body temperature, ° C.

T_(wh-c)=wheel temperature at the contact surface with rotor, ° C.

H_(hat)=height of rotor mounting hat, m (reference number 36 is FIG. 4)

Th_(1/2d)=half thickness of rotor disk, m

D_(d-h)=the distance between the disk middle circle and the mounting hatmiddle circle (FIG. 4.), m (reference number 34 in FIG. 4.)

In addition, we can define the following two quantities, the conductanceof the rotor (Conductance_(rotor)) and the conductance of the hat(Conductance_(hat)), using the parameters defined for the heatdissipation equation, above:

$\begin{matrix}{{Conductance}_{rotor} = {\frac{k_{r}A_{cross}}{H_{hat} + {Th}_{1\text{/}2d} + D_{d - h}}{Watts}\text{/}{^\circ}\mspace{14mu} {C.}}} & (4) \\{{Conductance}_{hat} = {\frac{k_{r}A_{cross}}{H_{hat}}{Watts}\text{/}{^\circ}\mspace{14mu} {C.}}} & (5)\end{matrix}$

In a preferred embodiment, a disk braking system has a rotor that has aconductance of greater than 4 W/° C. when used for stopping a movementwith a maximum (270 kJ) kinetic energy loaded on the brake system. Forstopping a movement with higher kinetic energy, the conductance shouldbe increased proportionally.

Also, in a preferred embodiment, a disk braking system has a rotor hatthat has a conductance of greater than 8 W/° C. when used for conductinga maximum heat converted from 270 kJ kinetic energy at once from therotor disk to a contacted wheel. For conducting a greater heat flow, theconductance should be increased proportionally.

Example

A 2002 Dodge Neon passage car has 1,542 kg or 15,129 Newton GVWR, 70%braking on front brakes, 85% heat distribution onto rotor, 15% ontopads, 8% tire slip. The car decelerates from a speed of 128.7 km/h or35.76 m/s without brake lockup. The entire vehicle braking energy is

$E_{b} = {\frac{\left( \text{15,129} \right)(35.76)^{2}}{2(9.81)} = {{\text{986,067}\mspace{14mu} {Nm}} = {0.274\mspace{14mu} {kWh}}}}$

The converted braking heat absorbed by one front brake is

E _(b-fr)=(0.274)(1−0.08)(0.70)(0.5)(0.85)=0.075 kWh=270 k)

The Dodge Neon disc brake has an aluminum body with k_(r)=166 W/(m° C.),a mounting hat with wall cross section 29.35 cm², hat height 3.81 cm,disc thickness 2.03 cm, and D_(d-h) 1.78 cm. Its rotor conductance andhat conductance are 0.00639 kW/° C. and 0.0128 kW/° C. respectively.The heat stored in the connected wheel is then dissipated by convectivecooling of outer wheel surfaces.

q _(wh) =h _(wh) A _(wh)(T _(wh-A) −T _(∞))  (6)

Where

q_(wh)=heat dissipation by convection of wheel surfaces, Joules/hour

h_(wh)=heat transfer coefficient of convection at wheel outer surfaces,Joules/(hour*m²*° C.)

A_(wh)=wheel outer surface area, m²

T_(wh-A)=average wheel temperature, ° C.

Proper design of disk brake and wheel shapes and dimensions and properselection of materials can make the Conductive cooling of the presentinvention, q_(cond) and q_(wh), much greater than q_(vent), for atraditional vented disk brake. This results in the wheel acting as themain heat sink and radiator, and lower brake working temperatures, up toseveral hundred degrees lower than temperatures reached at identicalbraking conditions by conventional cast iron disk brakes. Lower workingtemperatures reduce the pad wear considerably. All passenger cars,except for very small ones, use vented disk brakes for their front brakeapplications because they can take heavier duty. Unfortunately, thevents of the vented disk brakes of cast iron rust readily and get airblocked quickly, causing their heat dissipation capabilities declinedramatically after a moderate period of use. The preferred embodimentdescribed above makes nonferrous metal based and solid (not vented) diskbrake suitable for front brake applications of most passenger cars. Thispreferred embodiment of disk brake does not rely on vents, which haveproven so problematic, for heat dissipation and does not rust readily,resulting in consistent and excellent capability of heat dissipationduring its entire life. The invented disk brake is also suitable forrear brake applications. The parking brake shoes, which contact the rearbrakes on the interior surface of the hat side wall, can be made ofsofter material, as they are contacting an aluminum alloy, which issofter than the cast iron that similar pads contact in currentlyavailable rear disk brakes.

In one preferred embodiment, the disk brake and wheel assembly canabsorb and dissipate heat during repeated 100 kph (kilometer per hour)0.9 GVWR (deceleration of gross vehicle weight rating at 0.9gravitational constant) braking without exceeding 480° C. GVWR is theweight that a vehicle is designed to carry. The GVWR includes the netweight of the vehicle, the weight of passengers, fuel, cargo, andadditional accessories.

Example

A brake rotor's performance is evaluated quantitatively using a brakedynamometer. It can simulate precisely the brake working conditions andobtain the brake's response as in a real vehicle, such as GVWR, vehicleweight center, wheel rolling radius, static and dynamic wheel loads,wheel inertia, vehicle speed, deceleration speed, stop distance,pressure on brake pad, friction coefficient, and rubbing surfacetemperatures of inboard pad, outboard pad and rotor before and after astop. Brake fade test is a standard test procedure to evaluate thetemperature performance of a brake rotor and pads by 15 continuous stopsat GVWR, 120 kph speed, 0.3 g deceleration, and 45 second stopintervals.

A SCA solid brake rotor for the 2002 Dodge Neon front brake use with analuminum wheel mounted together has been tested on a brake dynamometerby a commercial brake testing lab following the FMVSS-135 certificationtest procedure. The fade test included in the FMVSS-135 certificationtest shows that the final temperature of the rotor rubbing surface is365° C. and 150° C. lower than the final pad temperature immediatelyafter the 15th stop. In contrary, the final rotor temperature of thecorresponding cast iron vented rotor is 569° C. and 144° C. higher thanthe final pad temperature at the identical testing conditions. It showsthat the SCA brake rotor surface temperature is 204° C. cooler than thecorresponding cast iron brake rotor surface temperature under identicalfade test conditions. The corresponding cast iron brake rotor meansidentical outer dimensions in comparison with the SCA brake rotor.

Fabrication

Referring to FIG. 2, FIG. 2 a, FIG. 4 a and FIG. 4 b, in a preferredembodiment, rotor 10 is manufactured by producing three steel claddingwork pieces 30′, each in the shape of a 118° arc, and forming a set ofthrough cuts 34 and step cuts 15.

A binder, preferably organic, such as rosin, gum, glue, oil, dextrin,acrylic, cellulose, syrup, phenolic, or polyurethane, is applied to aportion of said preliminary cladding work piece 30′ evenly or in apredetermined pattern. As an alternative embodiment, the binder isblended with additives. These additives may consist of metal, metaloxide and/or carbon particles in the size range from 0.1-500 μm,preferably 1-147 μm, in the binder and additive weight ratio preferably1:2 to 1:10.

Metal beads 40 (FIG. 3), which may be of either regular or irregularshapes, adhere on the binder-applied surface 41 of the preliminarycladding work piece 30′. The regular or irregular shapes may includespherical, cylindrical, polyhedral, ellipsoidal, T-shape, I-shape,L-shape, V-shape, screw, cone, staple, and other shapes which cangenerate mechanical interlocking. Equal-size metal spheres of 2-20 mm indiameter or 3.14-314 mm² in cross-section are used in one preferredembodiment. These metal beads 40 adhere on the binder-bearing surface 41in a predetermined distribution pattern in conjunction with the saidslot 34 pattern to arrange the slots 34 between beads to reduce thermalstress between beads during fabrication and service. Alternatively,these metal beads 40 adhere on the binder-bearing surface 41 in otherdistribution patterns (FIG. 3 a and FIG. 3 b), with pairs of beadsjoined together in the embodiment of FIG. 3 a and triplets of beadsjoined together in FIG. 3 b. This bead-to-bead bonding increases therigidity of the preliminary cladding work piece 30′, thereby avoidingthe potential problem of cladding 30 warping during its work life, dueto the extremes of pressure and temperature to which it is exposed.

Alternatively, binder may be applied to the beads 40, rather than, or inaddition to, the cladding workpiece 30′. The distance between beads ispreferably 1.5-10 times of said bead's diameter.

The workpiece 30′, now including the binder and the beads 40, is loadedinto a furnace. At an elevated temperature, the metal oxide reduces bycarbon if metal oxide powder is used, the binder and possibly a portionof the beads 40 and the surface material of cladding workpiece 30′, forma transient metal liquid. The transient metal liquid forms necks 42(FIG. 4 a) on the beads 40. Due to atomic diffusion of elements in themetal necks to adjacent regions, the metal necks become solid at saidelevated temperature. The cross-sectional diameter of a metal neck 42 issmaller than the bead's diameter, preferably ⅓-⅔ of the bead's diameter.After cooling, the beads 40 are welded onto the preliminary claddingworkpiece 30′ through the metal necks 42. As an alternative embodiment,the binder itself forms metal liquid and builds metal necks at anelevated temperature. The metal necks become solid after cooling.

The cladding workpiece can be further shaped by bending, straightening,punching, drawing or welding. The metal beads 40 can be deformed bypressing to form them into shapes better adapted for mechanicalinterlocking. The workpiece 30, is coated with a second metal which canform metallurgical bonding or interface compounds with both steel and athird metal. The second metal can be selected from Cu, Zn, Ni, Cr, Al,Fe, Si, Mn, Mg, Ti and their alloys. The workpiece is coated partiallyor entirely by chemical vapor deposition, physical vapor deposition,thermal spray coating, plating, spraying, brushing, or dipping.

The cladding workpiece is then inserted into a sand or metal mold. Thethird metal 32 (FIG. 1), preferably an aluminum alloy, is melted andcast into this mold to form a solid disk brake with the claddingworkpiece 30′. Any metal casting methods commonly used by the metalcasting industry, such as green sand casting, die casting, squeezecasting, permanent mold casting, core-making and inserting, investmentcasting, lost foam casting, and others, can be used in this invention.During casting, the molten third metal 32 is poured into the mold sothat it flows about and covers the beads and reacts with the secondmetal and permits the molten third metal 32 to cool. The first metalsurface, including the surface of the beads 40 and the necks 42, thecladding workpiece 30′, and the step cut 15 surface bonds with the thirdmetal body 32 in the combination of metallurgical bonding and mechanicalinterlocking, such as the third metal catches both the necks 42 of beads40 and the step cuts 15. The resulting disk brake is heat-treated torelease residual stress and reduce potential thermal stress while inservice, machined to produce the final product with the requireddimensions and enhanced properties on the rubbing surfaces, and paintedwith a high temperature paint in part to prevent salt corrosion.Referring to FIG. 4 b, in an alternative embodiment, the resulting diskbrake is machined less on the radially inner edge of cladding 30, tocreate a narrow rim 33, which enhances the rigidity of the machinedcladding 30 near its inner edge.

Referring to FIG. 5, in an alternative preferred embodiment, widercladding slots 50 are cut to allow molten third metal 32 into the slots50 during casting. After machining, the rubbing surfaces present a steeland aluminum hybrid structure as shown in FIG. 5. If carbon-kevlar padsare used such, the friction coefficient can be further increased toshorten stop distance.

Referring to FIG. 6, in a preferred embodiment, the inwardly facingsurface of hat top wall 12″ is thermally and sonically separated fromthe bearing hub 60 by a thin gasket 62, preferably made of polytetrafluoroethylene. Gasket 62 also prevents the rotor 10 from stickingto the bearing hub 60 by way of a rust buildup. As another alternativeto using a gasket 62, poly tetrafluoroethylene can be coated on the hattop wall 12″ inwardly facing surface.

While a number of exemplary aspects and embodiments have been discussedabove, those possessed of skill in the art will recognize certainmodifications, permutations, additions and sub-combinations thereof. Itis therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such modifications,permutations, additions and sub-combinations as are within their truespirit and scope.

1. An automotive disk brake assembly installed in an automobile having awheel, comprising: (a) a floating caliper supporting an inner and outerbrake pad; (b) a brake rotor having a disk, and a hat, and wherein saidhat is bolted to said wheel; (c) a hydraulic cylinder adapted to pushsaid inner brake pads into said disk surface, thereby causing saidfloating caliper to move so as to bring said outer brake pad intocontact with said disk surfaces; (d) wherein said rotor is made at leastin part of a material having a thickness and a coefficient of thermalexpansion and a thermal conductivity, such that a complete 100 kilometerper hour, 0.9 gross vehicle weight braking causes said disk to expand inthickness by at least 0.10 mm and to cool to shrink in thickness,relative to its expanded thickness, by at least 0.05 mm within 60seconds of the cessation of braking, in an ambient temperature of lessthan 30° C.
 2. The disk brake assembly of claim 1, wherein said materialhas a coefficient of thermal expansion of greater than 10.44×10-6/° C.3. The disk brake assembly of claim 1, wherein said material has acoefficient of thermal expansion of greater than 19.8×10-6/° C.
 4. Thedisk brake assembly of claim 1, wherein said disk is clad in steel atsurface area contacted by said pads.
 5. The disk brake assembly of claim1, wherein said assembly is mounted in an automobile having axlebushings and wherein said hat is set about one of said axle bushings andwherein a heat barrier separates said axle bushing from said hat.
 6. Thedisk brake assembly of claim 5, wherein said heat barrier is made ofpoly tetrafluoroethylene.
 7. The disk brake assembly of claim 1, furthercomprising a thermal coupler positioned between said hat and said wheel,to increase heat transfer from said hat to said wheel.
 8. The system ofclaim 1, further comprising applying a thermal conductive paste placedbetween said hat and said wheel contact to increase heat transfer.
 9. Adisc brake rotor, comprising: (a) mounting hat; and (b) solid disc,rigidly affixed to said mounting hat, and including: i. a transversedimension core, made of a first metal; ii. two rubbing-surfacecladdings, set on either transverse side of said core, said claddingsmade of a second metal and having a thickness of 1-10 mm, and furtherdefining physical engagement features; iii. a third metal interposedbetween said first metal and said second metal; and iv. wherein saidsecond metal bonded with said first metal metallurgically through saidthird metal and mechanically by said engagement features.
 10. The diskbrake rotor of claim 9, wherein said engagement features include stepcuts formed in said claddings, and filled with said first metal.
 11. Thedisk brake rotor of claim 9, wherein said engagement features furtherinclude radially-oriented through slots in said cladding, into whichsaid first metal has intruded.
 12. The disk brake rotor of claim 11,wherein said engagement features include beads arranged substantiallymedially between said through slots.
 13. The disc brake rotor of claim11, wherein said engagement features include beads arranged with groupsof beads in mutual contact, to increase the rigidity of saidrubbing-surface cladding.
 14. A method of fabricating a disk for a diskbrake system, comprising: (a) forming a cladding workpiece having afirst major external surface defining engagement features; (b) coatingsaid first major external surface with a second metal; (c) providing amold, defining an interior shape of a rotor; (d) inserting said claddingworkpiece into said mold; (e) providing a molten third metal; and (f)pouring said molten third metal into said mold so that it engages tosaid engagement features and reacts with said second metal andpermitting said molten third metal to cool, thereby forming a disk madeof said third metal, which is metallurgically bonded and mechanicallyinterlocked to said cladding workpiece.
 15. The method of claim 14,wherein said step of inserting said cladding workpiece into said mold,further includes inserting additional cladding workpieces into saidmold.
 16. The method of claim 14, wherein said cladding workpiecedefines radial slots, adapted to ameliorate the effects of thermalexpansion of said cladding workpiece.
 17. The method of claim 16,wherein said step of pouring said molten third metal into said mold isperformed so as to fill said radial slots.
 18. The method of claim 16,wherein said engagement features include beads affixed onto saidcladding workpiece, said beads arranged medially between said radialslots.
 19. The method of claim 14, wherein said engagement featuresinclude beads affixed onto said cladding workpiece.
 20. The method ofclaim 14, wherein said engagement features include step cuts formed intosaid cladding workpiece.
 21. The method of claim 14, further comprisingheating said disk to release residual stress caused by fabrication andreduce potential thermal stress induced in service.
 22. The method ofclaim 14, further comprising machining said disk to a specified shapeand dimensions.
 23. The method of claim 14, further comprising machiningsaid clad disk brake to a specified shape and dimensions having a steeland aluminum hybrid surface characteristic.
 24. The method of claim 14,further comprising machining said clad disk brake, to have anincreased-thickness inner rim, to maintain the rigidity of said claddingworkpiece.
 25. The method of claim 14, further comprising painting saiddisk brake partially with a high temperature paint.
 26. A disk brakingsystem having a rotor that has a conductance of greater than 2 Watts/°C.
 27. The system of claim 26, having a rotor that has a conductance ofgreater than 3 Watts/° C.
 28. The system of claim 26, having a rotorthat has a conductance of greater than 4 Watts/° C.
 29. A disk brakingsystem having a rotor hat that has a conductance of greater than 4Watts/° C.
 30. The system of claim 29, having a rotor hat that has aconductance of greater than 6 Watts/° C.
 31. The system of claim 29,having a rotor hat that has a conductance of greater than 8 Watts/° C.